Complex Servicing Of SONY CRT TV With Tips & Tricks For Easy Troubleshooting
MAKE AND MODEL NO: Sony KV-G21PD1 CRT TV
COMPLAINT REPORTED: Dead
HISTORY: This CRT TV belongs to my neighbor. He reported that only dark screen was visible and not even the LED was getting on. I opened the set in their house, did a thorough cleaning of the inside, discharged the anode for a possible charge and dismantled the PCB. Noticed that the board was modified to work from a separate SMPS board which was found tied to one side of the cabinet. The original SMPS in the board has been bypassed by this external power supply. SMPS Transformer, STR along with a couple of other components were missing in the power supply section. Brought the board home for thorough cleaning and troubleshooting.
TROUBLESHOOTING, RECTIFICATION, RESTORATION AND MODIFICATIONS DONE:
Section – 1 – Troubleshooting: Retouched a few dry solder joints found on the Board. Then disconnected the B+ line jumper going to FBT primary, the other end of which goes to Collector Horizontal Output Transistor. Loaded a 100W Bulb in its place and switched on the set. Checked the voltage present at the output, it was ok. As the CRT Tube that I have is not compatible with Sony, which uses Trinitron Tube, pins of which are different, I could not connect the board to the Testing Tube. Brought the TV to my home with the help of the neighbor, in his cycle. Connected the Board with the same complaint that was reported. Checked the B+ and noticed that it was dropping very low. I realized that something was shorting in the FBT section. I removed the Horizontal Output Transistor (HOT) and checked it. It was ok. Looked for any shorts in diodes used in the secondary of the FBT. Could not find any. Connected an LED between the Base and emitter points of the HOT and switched on. The LED remained LIT indicating that the oscillation was taking place. Everything was OK upto the FBT. Suspicion therefore was on the FBT, though the Ring Tester showed ok. It can always fail when a load is given, which is quite common. Removed the FBT, grounded the pin that goes to collector of the HOT through a wire and supplied B+ to the other pin, which then dropped. A clear indication of short in FBT. An easy method to check that. If , however it does not drop, as there is no load on the output, we can connect a 45 to 60W bulb to its 140V output that goes to RGB drive. That is another easy way to correctly check the FBT.
Section – 2 – Rectifications (a): Obtained a replacement FBT and new H-out Transistor. The old FBT had only two wires coming out, one for Anode and another for Focus, as the Screen voltage is taken out through a pin underneath. But the new one had three wires; Anode, Screen and Focus. Loaded the Board to CRT after replacing the FBT and HOT (D1878), with modifications in Main PCB and CRT PCB (described later in the article). The Blue Raster came on indicating that the TV was now working. Discharged the anode and tank capacitor and removed the board for further work on it.
Rectifications (b): Replaced all the electrolytic capacitors on the board. Did dry solder patch up without leaving even one solder point on both the boards. Decided to restore the original SMPS of this Board, for which I obtained the circuit diagram from my Techie friends and also the details of missing components; i.e., SMPS Transformer, Diode and a resistor. Got one spare SMPS Tx from another friend.
Section – 3 – Restoration of Power Supply: Looked for any defective components in the SMPS primary. Found one Diode showing resistance in both directions. Replaced it. Fixed the SMPS STR6707N, Diode D607 and resistor R606. Checked with circuit diagram and ensured that everything was in its place and position. Powered the SMPS giving the load at the B+ rail (of-course, after removing the jumper to the FBT) and was happy to note that the B+ was showing 115V! What a relief it was to see that the original power supply was restored and the hanging external SMPS board was relieved of its services. Imagined the happiness of a person who got relieved of his externally hanging bypass systems after restoration of an important organ!
Section – 4 – Modifications done: Removed one end of the High Voltage diode from the FBT at the Main Board so as to disable the supply wire that goes to the CRT PCB. Disconnected one end of two resistors on the CRT Board and ensured that the Screen Voltage Wire of the new FBT is linked to Grid 2 of the CRT, bypassing the potentiometer on it. Replaced its filter capacitor as a preventive maintenance.
TESTING DONE: After checking that everything was ok, restored the B+ supply to FBT and loaded the board to CRT. Connected a video input. Adjusted the Screen and Focus voltages to get a peak performance. The picture was so clear like a new TV. Thus a complex servicing of a CRT TV came to an end and satisfaction intensified got added to its collection!
USEFUL AND CONNECTED LINKS: All about CRT tubes : https://www.repairfaq.org/sam/crtfaq.htm
How To Completely Check The High Voltage Circuit In CRT Moitor/Television: http://www.electronicrepairguide.com/high-voltage-circuit.html
Recommended books : https://jestineyong.com/crt-tv-repair-ebook/
https://jestineyong.com/crt-television-troubleshooting-guide/
This article was prepared for you by Parasuraman Subramanian from India. He is 70 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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You may check on his previous repair article below:
https://jestineyong.com/rusted-components-found-in-kemai-usb-radio-model-md-1800ur/
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Albert van Bemmelen
July 21, 2020 at 7:05 pm
Interesting way how you checked the Horizontal Oscillator with a led on the Base and emitter points of the H.O. output transistor. (Since you didn't even need or use an oscilloscope this way). And how easy you say it is possible to check the FBT by connecting a 45 to 60W bulb to its 140V output that goes to RGB drive. And good to know that the (Blue) Ring Tester test is not always correct because the FBT still can fail when a load is given.
Parasuraman S
July 21, 2020 at 8:46 pm
Yes, a lot of new lessons learnt in the process! Many thanks for your detailed comments!
Waleed Rishmawi
July 21, 2020 at 9:32 pm
Very intense repair. I hope it was worth it. A lot of time and money spent. Have a blessed day
Parasuraman S
July 21, 2020 at 11:07 pm
It was worth it, as I have a very satisfied neighbour! Moreover, he paid for everything including my service charges!
Bijoy Ghimiray
July 21, 2020 at 10:08 pm
Pls continue to update us with your valuable experience and outstanding performance.
Parasuraman S
July 21, 2020 at 11:08 pm
Many thanks! Knowledge and experience get a better shine, when shared!
Henrique J. G. Ulbrich
July 22, 2020 at 12:48 am
Great, Parasuraman. I would like to have your patience.
Parasuraman S
July 23, 2020 at 7:50 am
Many thanks! Ok! Shall do an telepathic transfer! (LOL)
Lynn Blakely
July 22, 2020 at 8:48 am
Good Job Parasuraman S. Sony had to do some things different. The front ot the crt is straight up & down on the front. The glass on the front is thicker than conventional crt's. and heavier. If I remember correctly they used a single emitter in the neck of the tube to scan from to produce the scanning, also they used a different matrix to light up the phosphor of the primary colors. It's somewhat hard to remember some of the technology of the past. RCA said it can't be done. Sony proved them wrong. Thanks for your very complete repair.
Parasuraman S
July 23, 2020 at 7:52 am
Yes, Sony always does things that are quite uncommon and have made a mark of themselves exclusively! The main problem is getting spares! Many thanks for your analytical comments!
B K DEB
May 2, 2021 at 1:07 am
I have SONY wega trinitron tv CRT type.It has been running quite well till picture stopped display all of a sudden.Please advise where I can get it repaired.
Thanks,
BK DEB
Arshad
July 22, 2020 at 11:24 am
Thanks sir. Valubale information.
Parasuraman S
July 23, 2020 at 7:53 am
Many thanks!
Jithesh
July 22, 2020 at 12:21 pm
very many thanks to you sir, how simply explained these things! It is a very helpful article for beginners like me..... all the best sir....
Parasuraman S
July 23, 2020 at 7:53 am
Hi Jithesh! Thanks for taking the trouble of making a comment here!
Humberto
July 23, 2020 at 1:15 pm
Hi Parasuraman, I´ve really enjoyed reading your article. Congratulations.
Parasuraman S
July 23, 2020 at 3:39 pm
Many thanks! I am happy that you enjoyed the article!
Imoudu ONWUMAH
July 24, 2020 at 2:07 am
Hi Parasuraman,Thanks for ur detailed explanations on this repair.when it comes to crt tv repair,I don't know much,for I am a beginner.Now u have given me a vital info about Jestine e-book on crt t.v repair which I don't know before. He is my instructor thru some of his electronics repairs e-books.I will surely purchase this too. Thanks.
Parasuraman S
July 24, 2020 at 12:48 pm
I am happy that the article was of use to you. Yes, please do buy Jestine Yong's wonderful books. They are more than worth the money you pay!
Imran
July 27, 2020 at 8:57 am
Very nice fault finding tips. Thanks
Parasuraman S
July 28, 2020 at 7:22 am
Many thanks!
Joven Urbano
September 29, 2020 at 12:09 am
Very tedious repair job but patience prevailed. Job well done!
Rushdy
December 3, 2020 at 5:38 am
Dear Sir
Please Where can I find this product? Ultrasonic Car CD player .... I already bought it from Dubai but now can’t find ...please if you have factory address send it to me
Thank you
SANTOSH
May 10, 2021 at 6:33 pm
My sony 25 inch tv having model no. AR25M80 AND the FBT of it is blownoff. initially it was having 8-598-831-20 Nx 4009//c which was replaced by 8-598-831-30 by tv technician but it failed within one year this month now I am not getting the FbT. PL ADVICE
Muraliraju
October 30, 2021 at 7:18 pm
Sir sony wega crt tv blue color problem. Red led 5 times blinking. Shown voltage for blue 1.38v, green 2.80v and red 2.95 so what is the problem
Thank you